Hard disk drives (HDD), particularly those that are used in mobile computers, have to be designed to withstand the rough usage typically seen in the mobile environment. The shock robustness of such drives has improved primarily in the ability to withstand large shocks during the nonoperating mode. Typically, when not operating the slider assembly, which includes the read and write elements of the HDD, is “unloaded” by moving the slider onto a ramp near the outer diameter of the disk. In this way, in the event of shock the slider does not contact the disk, which could otherwise damage the slider and/or disk.
Before the drive is assembled, a slider orientation parameter referred to as “roll static attitude” (RSA) is set to zero on average, while a parameter referred to as “pitch static attitude” (PSA) is set slightly above zero on average (typically 50–100 min). What this means is that the slider has a slight pitch relative to the load beam of the suspension (non-zero PSA), i.e., the leading edge of the slider is slightly closer to the disk than the trailing edge, whereas in the orthogonal dimension of roll the slider is parallel to the suspension (zero RSA, i.e., the radially outer edge of the slider is the same height as the radially inner edge).
One role of the PSA value is to impart a rotating moment force to the slider through the suspension stiffness. Therefore, by changing the PSA, the balance of forces is modified, and the slider will adjust its fly height to recover an equilibrium of forces. On current designs, increasing the PSA results in higher force acting on the trailing edge of the slider, causing the slider to fly closer to the disk.
The present invention makes the observation that PSA-induced torque is part of the balance of forces that determines the fly height of the slider. Specifically, a higher PSA pushes the trailing edge of the slider closer to the disk and decreases fly height, potentially to the point of the slider undesirably touching the disk. However, the present invention recognizes that a higher PSA is good for loading, because when the slider is loaded from the ramp to the disk, it can happen that the slider might touch the disk, and that if it touches at the leading edge the slider undesirably can pitch forward. With respect to the unloading process, the present invention understands that the force that is required to move (“snap”) the slider away from the disk, if high, can cause the slider to undesirably vibrate and potentially damage the disk during unloading.
As further recognized herein, it is also desirable to avoid the drawback of making it harder to “snap” the slider onto the disk, i.e., to quickly establish the desired close spacing between the slider and disk. Such a circumstance otherwise could lead to undesirable bi-stable fly height, wherein the slider, which ordinarily flies at, e.g., fifteen nanometers from the disk once the air bearing is established between the slider and disk, must fly above the disk at a much higher height (e.g., a micrometer) until such time as the air bearing is established, complicating slider position control. It is further observed that the PSA requirements for optimized loading are usually contrary to those required for unloading. Optimizing flying conditions can yield yet a different target PSA value. Recognizing this problem, the present invention is provided.